The 27-year-old Argenitina international scored both goals in a 2-1 win over Inter Milan which moved Napoli to the top of Serie A, with the former Real Madrid frontman having now scored 12 goals in 14 league games so far this season.
However, Sarri says there is still some untapped potential in the South American, as he told Sky Sport Italia: "It depends on him. If Higuain makes another step forward psychologically, then he can become an extra-terrestrial.
"He needs to be even more determined, because he can become even better."
Meanwhile, Sarri played down talk of a push for a first Italian title since 1989/90, insisting that it is far too early in the campaign to think about lifting Lo Scudetto.
He added: "There is no point talking now, there are another 72 points up for grabs, with 31 so far we haven't even guaranteed safety from relegation.
"Tomorrow the team will sit down and talk about what we can improve, not the table. We can't think that we are the best because we won a game."
Napoli lead the table by a single point from Inter, with Fiorentina a point further back in third place.
Reigning champions Juventus are also back in the frame after overcoming a slow start to the campaign to win five of their last six Serie A matches.